Print hammer actuator



Aug. 12, 1969 E. A. BROWN ET 3, 6

YRINT HAMMER ACTUATOR Filed Dec. :50, 1966/ LHHH IQ FIG.3

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INVENTORS EDGAR ALAN BROWN RICHARD H. DARLING ALBERT s. CHOU .By'

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DISPLACEMENT FIG.4

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ATTORNEY United States Patent US. Cl. 101-93 13 Claims ABSTRACT OF THE DISCLOSURE A print hammer actuator which provides a cycle of operation under control of an electrical signal for a rapid movement to the operative position and a rapid reversal and restore of a hammer to its ready position. The actuator comprises a magnetic core structure forming a. substantially closed path shaped to form two offset pole pieces. A resilient actuator member is mounted with one point fixed relative to the magnetic core structure and having a movable magnetic member attached to another point in a position so that the generation of a magnetic flux within the magnetic core structure attracts the movable member to position the actuator member in a ready position. A winding is provided on the magnetic core structure, and to select an operation of the print hammer the coil is energized to reduce the net flux in the magnetic path to essentially zero during the forward flight time of the hammer. The magnetic flux within the magnetic core structure then reattrac'ts the movable member to reposition the actuator member in a position ready for a subsequent cycle of operation.

CROSS-REFERENCE TO RELATED APPLICATIONS Actuator Driver Circuit by Edgar A. Brown and Richard H. Darling, filed Dec. 30, 1966, Ser. No. 606,311.

BACKGROUND OF INVENTION This invention relates to electromechanical actuators and more particularly to an actuator for a high speed print hammer.

The invention is particularly suitable for use in a printer operating with a data processing system. In printers of this type, it is desirable to obtain a high printing rate to efficiently utilize the data processing system. To obtain a high printing rate, the time required to actuate a print hammer and then to restore the hammer to the print ready position should be as short as possible. In addition, to obtain high print quality, the time during which the print hammer is at or near the printing surface should be as short as possible. It is therefore the principal object of this invention to provide a print hammer capable of operating at a very high cycle rate.

It is another object of this invention to provide a print hammer having the least amount of the magnetic circuit in the movable part of the system.

It is a further object of this invention to provide a print hammer which is under positive control at all times during a print cycle.

Briefly, according to the invention, the actuator comprises a magnetic core structure forming a substantially closed path shaped to form two olfset pole pieces. A resilient actuator member is mounted with one point fixed relative to the magnetic core structure and having a movable magnetic member attached to another point and positioned so that the generation of a magnetic flux within the magnetic core structure attracts the movable member to form a complete magnetic circuit and position the actuator member in a ready position and a winding is provided for selective energization to release the mov- 3,460,469 Patented Aug. 12, 1969 able magnetic member so that the actuator member produces one cycle of movement.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings.

FIGURE 1 is a left side view of an array of print hammer actuators embodying the present invention.

FIGURE 2 is a top view of an array of print hammer actuators embodying the present invention.

FIGURE 3 is a front view of an array of print hammer actuators embodying the present invention.

FIGURE 4 is a graph showing displacement on a time scale for the print hammer of the present invention.

FIGURE 5 is a schematic diagram of the driver circuit for the print hammer actuator.

Referring to the embodiment of the invention shown in the drawings, a plurality of print actuators 10 are shown mounted in a side-by-side array. Each of the actuators comprises a magnetic core structure 12 forming a substantially enclosed magnetic path. Resilient actuator member 16 is fixed at one end and mounted for movement to the operative position to print a character, and a movable magnetic member 14 is coupled to the actuator member 16 and positioned to complete the magnetic circuit formed by core structure 12. The operation of actuator member 16 is controlled by a first winding 18 which is wound to enclose the core structures 12 of all of the actuator assemblies 10. A second Winding 20 is provided for each of the actuator assemblies 10. Energization of first winding 18 by a suitable direct current voltage produces a magnetic flux in the core structure 12 and attracts movable member 14 to thereby store energy in resilient actuator member 16. Selective operation of actuator member 16 is provided by energizing second winding 20 by a suitable voltage. Winding 20 is energized so that the flux produced by this winding op mses the flux in the magnetic path produced by wind ing 18 in the actuator 10 selected. When the magnetic force on member 14 is reduced below the force produced by member 16, the member 16 is propelled to print a character by impacting a print character (not shown) into a suitable printing surface backed by a suitable platen member (not shown). The voltage to coil 20 is removed at this time, the actuator member rebounds from the platen member and the flux generated by winding 18 reattracts movable member 14 to the print ready position again so that the actuator member is then in position to start another print cycle.

Thus, it can be seen that there is provided a print hammer which does not require a mechanical restore cycle which contributes to a faster print cycle. In addition, the print hammer is under positive control throughout the cycle. The print hammer is under control of the hold Winding 18 during the print ready part of the cycle while winding 20 provides the control to release the print hammer to the print position. The movement of the print hammer during this period of the cycle is controlled by the spring member 16 releasing the potential energy which was stored in this spring by movable member 14 being attracted by winding 18. As the hammer rebounds from the printing surface, Winding 18 reattracts the hammer to the print ready position.

There is a minimum mass in the moving system so that the low inertia of the moving parts also contributes to a fast print cycle. Movable member 14 is the only part of the magnetic circuit which is in the moving system. This arrangement provides the advantage that member 14 and all other parts of the magnetic circuit can be designed considering only their magnetic characteristics, thereby resulting in a highly eflicient magnetic circuit while, at the same time, designing actuator member 16 strictly for its mechanical properties, thereby also producing a mechanical system of high efficiency.

Referring to the embodiment of the print hammer actuator shown in the drawing, the core structure 12 comprises a substantially closed path formed of a suitable ferromagnetic material. The core structure 12 may be fonmed with a U-shaped member 22 and a substantially straight member 24 attached to substantially enclose the open end of member 22. The core members 22 and 24 are mounted to form laterally offset pole pieces 26 and 28. Movable magnetic member 14 is selectively positionable to complete the magnetic path.

Coil winding 18 functions to attract magnetic member 14 to pole piece 26 when coil member 18 is energized by a suitable voltage. Coil member 20 is provided to select the time at which actuator member 16 is moved to the operative position by cancelling the flux generated in core structure 12 by coil member 18 to release member 14 from pole piece 26.

In the embodiment shown, actuator member 16 comprises a print hammer constructed of a resilient material such as spring steel. The print hammer is attached at its lower end by means of screws 30 to core member 22. The upper end of the spring member is turned at substantially a right angle to form a hammer striking surface 32. Intermediate the ends of the spring member 16, an adjustable fulcrum 34 is provided. Movable member 14 is attached to the upper end of spring member 16 opposite striking surface 32.

Movable magnetic member 14 is designed to provide the necessary area facing pole piece 26, and the side area facing pole piece 28 is increased considerably above the pole face area so that the side force is less than the force of attraction between pole piece 26 and movable member 14. In addition, magnetic reluctance between member 14 and pole piece 28 is less than the reluctance between member 14 and pole piece 26. The larger area and lower reluctance is efiective in reducing wear between member 14 and pole piece 28.

To reduce the inertia of the moving parts to the minimum, movable member 14 is made wedge-shaped since this shape provides suflicient magnetic material to produce an efficient magnetic circuit. This arrangement has the additional advantage that the print hammer is self-damping. This is due to the fact that when member 14 is being attracted at first very few flux lines are linked through movable member 14. As the hammer is restored progressively, more flux lines are linked through the side area of member 14 and pole piece 28, producing a side force and results in rubbing of movable member 14 against pole piece 28 which dissipates the energy through conversion of the energy to heat due to the frictional engagement of movable member 14 and pole piece 28.

Since the motive force for movement of the print hammer to the operative position is provided by the extension of the spring, it is necessary to obtain a high efiiciency in the conversion of the potential energy stored in the spring due to the attraction of magnetic member 14 to kinetic energy in moving the print hammer to the operative position. The efliciency of the conversion of energy depends on the spring being essentially at a high constant stress value and also that the spring has a uniform energy density throughout its length. In addition, any mass in the system other than the spring member itself should be kept to a minimum. The ideal case for an efficient transfer of energy is for the spring member to have a radius of curvature and a constant width. The provision of adjustable fulcrum 34 and a slight angle on the surface of pole piece 26 provides a close approximation to a radius of curvature on the spring when movable member 14 is attracted to pole piece 26. Small adjustments in the position of fulcrum 34 may be made by screw 36 to provide for altering the flight time of the hammer.

To select an operation of the print hammer, coil member 20 is energized to reduce the net flux in the magnetic path to essentially zero during the forward flight time of the hammer. Thus, as seen in FIGURE 4, the print hammer provides a cycle of operation under control of an electrical signal of a rapid movement to the operative position and a rapid reversal and restore of the hammer to its original position.

The actuator may be controlled by any suitable elccironic driving means. A suitable driving means provides initially a large current for a short duration which drops to a lower level of current for a further period of time and then drops to essentially zero, thereby yielding essentially a square wave of flux.

In a specific embodiment of the hammer actuator comprising the invention, the actuator is capable of operation with suflicient energy to print at least five copies at a rate of 650 cycles/sec. Referring to FIGURE 4, the print cycle comprises a forward stroke (from energizing to print) of approximately 700 microseconds, and a restore stroke r (from print to print ready) of approximately 850 microseconds which gives a rate of 650 cycles/second.

One suitable driving means is shown schematically in FIGURE 5. In this circuit, winding 20 is tapped to form coil portions 20t and 2011. A suitable voltage source is coupled across coil 20, a capacitor 38 and switching means 40. In addition, a resistor 42 is coupled across winding portion 20b and capacitor 38.

In this circuit when switching means 40 is closed, capacitor 38 starts charging and a large current fiows through both winding portions 20b and 20!. As capacitor 38 accumulates more and more charge, the current starts to drop. At the same time, some current passes through resistor 42 and winding 20L These two currents are additive to produce the large initial current.

When capacitor 38 becomes fully charged, the only current flow is through resistor 42 and winding 201 and a lower steady state current is produced. When switching means 40 is opened, the charge on capacitor 38 causes current to flow in the loop including winding 20]) and resistor 42, thereby providing a magnetic field in addition to the bias field of winding 18 assisting in restoring actuator 16 to its ready position.

The control circuit is described in greater detail and claimed in application Ser. No. 606,311, filed concurrently herewith, entitled Actuator Driver Circuit, by Edgar A. Brown and Richard H. Darling.

While the invention has been particularly shown and described with reference to a prefer-red embodiment thereof, it will be understood by those skilled in the art that various changes in the form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. An electromechanical actuator for selectively producing a cycle of operation from a ready position to the operative position and back to the ready position comprising:

a magnetid core structure forming a substantially closed path shaped to form two offset pole pieces;

a movable magnetic member;

a resilient actuator member fixed relative to said magnetic core structure at one point thereof and having said movable magnetic member attached to another point thereof;

a winding on said magnetic core structure;

means for generating a magnetic flux in said magnetic core structure to attract said movable magnetic member to said pole pieces and hold said actuator member in said ready position; and

means to selectively energize said Winding for a predetermined time to generate a flux opposing said flux in said magnetic core structure to release said movable magnetic member from said pole pieces so that said actuator member produces one cycle of movement.

2. The electromechanical actuator according to claim 1 wherein said movable magnetic member comprises a wedge-shaped member having one face substantially parallel to its direction of motion and a second face substantially normal to its direction of motion.

3. An electromechanical actuator for selectively producing a cycle of operation from a ready position to the operative position and back to the ready position comprising:

a magnetic core structure forming a substantially closed path shaped to form two laterally offset pole pieces;

a movable magnetic member;

a resilient actuator member fixed at one end relative to said magnetic core structure and having said movable magnetic member attached to the other end;

a first and a second winding on said magnetic core structure;

means for energizing said first winding to attract said movable magnetic member to said pole pieces and hold said actuator member in said ready position; and

means to energize said second winding for a predetermined time to generate a flux opposing said flux in said magnetic core structure to release said movable magnetic member so that said actuator member produces one cycle of movement.

4. The electromechanical actuator according to claim 3 wherein said movable magnetic member comprises a Wedge-shaped member having one face substantially parallel to its direction of motion and a second face substantially normal to its direction of motion.

5. A print hammer actuator for selectively producing a cycle of operation from a ready position to the operative position and back to the ready position comprising:

a magnetic core structure forming a substantially closed path shaped to form two ofiset pole pieces;

a movable magnetic member;

a resilient print hammer member fixed relative to said magnetic core structure at one point thereof and having a striking surface at another point thereof;

means for attaching said movable magnetic member to said print hammer opposite said striking surface thereof;

a winding on said magnetic core structure;

means for generating a magnetic flux in said magnetic core structure to attract said movable magnetic member to said pole pieces and hold said actuator member in said ready position; and

means to selectively energize said winding for a predetermined time to generate a flux opposing said flux in said magnetic core structure to release said movable magnetic member from said pole pieces so that said print hammer member produces one printing cycle.

6. The print hammer actuator according to claim 5 wherein said movable magnetic member comprises a wedge-shaped member having one face substantially parallel to its direction of motion and a second face substantially normal to its direction of motion.

7. A print hammer actuator for selectively producing a cycle of operation from a ready position to the operative position and back to the ready position comprising:

a magnetic core structure forming a substantially closed 65 path shaped to form two laterally offset pole pieces; a, movable magnetic member having a wedge-shaped cross-section;

a resilient print hammer member fixed at one end relative to said magnetic core structure and having a hammer portion formed on the other end thereof;

means for mounting said movable magnetic member to said hammer portion of said print hammer member so that the thinnest part of said wedge-shaped crosssection extends toward said hammer portion;

a first and a second winding on said magnetic core structure;

means for energizing said first winding to attract said movable magnetic member to said pole pieces and hold said print hammer member in said ready position;

means fixedly mounted adjacent to said print hammer member to engage said print hammer member intermediate the ends thereof for adjusting the curvature of said print hammer member in the ready position; and

means to selectively energize said second winding for a predetermined time to generate a flux opposing said flux in said magnetic core structure to release said movable magnetic member so that said print hammer member produces one printing cycle.

8. The electromechanical actuator according to claim 1 further comprising fulcrum means for engaging said actuator member intermediate said one and another points to produce a curvature in said actuator member when in said ready position.

9. The electromechanical actuator according to claim 8 further comprising means for adjusting said fulcrum means relative to said actuator member for adjusting the curvature of said actuator member in said ready position.

10. The electromechanical actuator according to claim 3 further comprising fulcrum means for engaging said actuator member intermediate said one and another points to produce a curvature in said actuator member when in said ready position.

11. The electromechanical actuator according to claim 10 further comprising means for adjusting said fulcrum means relative to said actuator member for adjusting the curvature of said actuator member in said ready position.

12. The electromechanical actuator according to claim 5 further comprising fulcrum means for engaging said actuator member intermediate said one and another points to produce a curvature in said actuator member when in said ready position.

13. The electromechanical actuator according to claim 12 further comprising means for adjusting said fulcrum means relative to said actuator member for adjusting the curvature of said actuator member in said ready position.

References Cited UNITED STATES PATENTS 2,687,088 8/1954 Hennessy et al. 10195 2,928,896 3/1960 Dirks 17834 2,940,385 6/1960 House 101--93 2,976,801 3/1961 Dirks 101-93 3,021,454 2/1962 Pickens 317148.5 3,049,990 8/1962 Brown et al. 101--93 3,126,823 3/1964 Benson 10193 3,172,352 3/1965 Helms 101-93 3,223,029 12/1965 Simshauser 101--93 3,359,921 12/1967 Arnold et al. 10193 WILLLAM B. PINN, Primary Examiner US. Cl. X.R. 335-209 

